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Bifunctional Molybdenum Polyoxometalates for the Combined Hydrodeoxygenation and Alkylation of Lignin‐Derived Model Phenolics
Author(s) -
Anderson Eric,
Crisci Anthony,
Murugappan Karthick,
RománLeshkov Yuriy
Publication year - 2017
Publication title -
chemsuschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.412
H-Index - 157
eISSN - 1864-564X
pISSN - 1864-5631
DOI - 10.1002/cssc.201700297
Subject(s) - hydrodeoxygenation , alkylation , chemistry , anisole , depolymerization , bifunctional , selectivity , organic chemistry , guaiacol , lewis acids and bases , catalysis
Reductive catalytic fractionation of biomass has recently emerged as a powerful lignin extraction and depolymerization method to produce monomeric aromatic oxygenates in high yields. Here, bifunctional molybdenum‐based polyoxometalates supported on titania (POM/TiO 2 ) are shown to promote tandem hydrodeoxygenation (HDO) and alkylation reactions, converting lignin‐derived oxygenated aromatics into alkylated benzenes and alkylated phenols in high yields. In particular, anisole and 4‐propylguaiacol were used as model compounds for this gas‐phase study using a packed‐bed flow reactor. For anisole, 30 % selectivity for alkylated aromatic compounds (54 % C‐alkylation of the methoxy groups by methyl balance) with an overall 72 % selectivity for HDO at 82 % anisole conversion was observed over H 3 PMo 12 O 40 /TiO 2 at 7 h on stream. Under similar conditions, 4‐propylguaiacol was mainly converted into 4‐propylphenol and alkylated 4‐propylphenols with a selectivity to alkylated 4‐propylphenols of 42 % (77 % C‐alkylation) with a total HDO selectivity to 4‐propylbenzene and alkylated 4‐propylbenzenes of 4 % at 92 % conversion (7 h on stream). Higher catalyst loadings pushed the 4‐propylguaiacol conversion to 100 % and resulted in a higher selectivity to propylbenzene of 41 %, alkylated aromatics of 21 % and alkylated phenols of 17 % (51 % C‐alkylation). The reactivity studies coupled with catalyst characterization revealed that Lewis acid sites act synergistically with neighboring Brønsted acid sites to simultaneously promote alkylation and hydrodeoxygenation activity. A reaction mechanism is proposed involving activation of the ether bond on a Lewis acid site, followed by methyl transfer and C‐alkylation. Mo‐based POMs represent a versatile catalytic platform to simultaneously upgrade lignin‐derived oxygenated aromatics into alkylated arenes.